DOLFINx 0.9.0
DOLFINx C++ interface
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IndexMap Class Reference

#include <IndexMap.h>

Public Member Functions

 IndexMap (MPI_Comm comm, std::int32_t local_size)
 Create an non-overlapping index map.
 
 IndexMap (MPI_Comm comm, std::int32_t local_size, std::span< const std::int64_t > ghosts, std::span< const int > owners)
 Create an overlapping (ghosted) index map.
 
 IndexMap (MPI_Comm comm, std::int32_t local_size, const std::array< std::vector< int >, 2 > &src_dest, std::span< const std::int64_t > ghosts, std::span< const int > owners)
 Create an overlapping (ghosted) index map.
 
 IndexMap (const IndexMap &map)=delete
 
 IndexMap (IndexMap &&map)=default
 Move constructor.
 
 ~IndexMap ()=default
 Destructor.
 
IndexMapoperator= (IndexMap &&map)=default
 Move assignment.
 
IndexMapoperator= (const IndexMap &map)=delete
 
std::array< std::int64_t, 2 > local_range () const noexcept
 Range of indices (global) owned by this process.
 
std::int32_t num_ghosts () const noexcept
 Number of ghost indices on this process.
 
std::int32_t size_local () const noexcept
 Number of indices owned by this process.
 
std::int64_t size_global () const noexcept
 Number indices across communicator.
 
std::span< const std::int64_t > ghosts () const noexcept
 
MPI_Comm comm () const
 Return the MPI communicator that the map is defined on.
 
void local_to_global (std::span< const std::int32_t > local, std::span< std::int64_t > global) const
 Compute global indices for array of local indices.
 
void global_to_local (std::span< const std::int64_t > global, std::span< std::int32_t > local) const
 Compute local indices for array of global indices.
 
std::vector< std::int64_t > global_indices () const
 Build list of indices with global indexing.
 
std::span< const int > owners () const
 The ranks that own each ghost index.
 
graph::AdjacencyList< int > index_to_dest_ranks () const
 Compute map from each local (owned) index to the set of ranks that have the index as a ghost.
 
std::vector< std::int32_t > shared_indices () const
 Build a list of owned indices that are ghosted by another rank.
 
std::span< const int > src () const noexcept
 Ordered set of MPI ranks that own caller's ghost indices.
 
std::span< const int > dest () const noexcept
 Ordered set of MPI ranks that ghost indices owned by caller.
 
std::array< double, 2 > imbalance () const
 Returns the imbalance of the current IndexMap.
 

Detailed Description

This class represents the distribution index arrays across processes. An index array is a contiguous collection of N+1 indices [0, 1, . . ., N] that are distributed across M processes. On a given process, the IndexMap stores a portion of the index set using local indices [0, 1, . . . , n], and a map from the local indices to a unique global index.

Constructor & Destructor Documentation

◆ IndexMap() [1/3]

IndexMap ( MPI_Comm comm,
std::int32_t local_size )

Create an non-overlapping index map.

Note
Collective
Parameters
[in]commMPI communicator that the index map is distributed across.
[in]local_sizeLocal size of the index map, i.e. the number of owned entries.

◆ IndexMap() [2/3]

IndexMap ( MPI_Comm comm,
std::int32_t local_size,
std::span< const std::int64_t > ghosts,
std::span< const int > owners )

Create an overlapping (ghosted) index map.

This constructor uses a 'consensus' algorithm to determine the ranks that ghost indices that are owned by the caller. This requires non-trivial MPI communication. If the ranks that ghost indices owned by the caller are known, it more efficient to use the constructor that takes these ranks as an argument.

Note
Collective
Parameters
[in]commMPI communicator that the index map is distributed across.
[in]local_sizeLocal size of the index map, i.e. the number of owned entries
[in]ghostsThe global indices of ghost entries
[in]ownersOwner rank (on comm) of each entry in ghosts

◆ IndexMap() [3/3]

IndexMap ( MPI_Comm comm,
std::int32_t local_size,
const std::array< std::vector< int >, 2 > & src_dest,
std::span< const std::int64_t > ghosts,
std::span< const int > owners )

Create an overlapping (ghosted) index map.

This constructor is optimised for the case where the 'source' (ranks that own indices ghosted by the caller) and 'destination' ranks (ranks that ghost indices owned by the caller) are already available. It allows the complex computation of the destination ranks from owners.

Note
Collective
Parameters
[in]commMPI communicator that the index map is distributed across.
[in]local_sizeLocal size of the index map, i.e. the number
[in]src_destLists of [0] src and [1] dest ranks. The list in each must be sorted and not contain duplicates. src ranks are owners of the indices in ghosts. dest ranks are the rank that ghost indices owned by the caller.
[in]ghostsThe global indices of ghost entries
[in]ownersOwner rank (on comm) of each entry in ghosts

Member Function Documentation

◆ comm()

MPI_Comm comm ( ) const

Return the MPI communicator that the map is defined on.

Returns
Communicator

◆ dest()

std::span< const int > dest ( ) const
noexcept

Ordered set of MPI ranks that ghost indices owned by caller.

Typically used when creating neighbourhood communicators.

Returns
MPI ranks than own ghost indices. The ranks are unique and sorted.

◆ ghosts()

std::span< const std::int64_t > ghosts ( ) const
noexcept

Local-to-global map for ghosts (local indexing beyond end of local range)

◆ global_indices()

std::vector< std::int64_t > global_indices ( ) const

Build list of indices with global indexing.

Returns
The global index for all local indices (0, 1, 2, ...) on this process, including ghosts

◆ global_to_local()

void global_to_local ( std::span< const std::int64_t > global,
std::span< std::int32_t > local ) const

Compute local indices for array of global indices.

Parameters
[in]globalGlobal indices
[out]localThe local of the corresponding global index in 'global'. Returns -1 if the local index does not exist on this process.

◆ imbalance()

std::array< double, 2 > imbalance ( ) const

Returns the imbalance of the current IndexMap.

The imbalance is a measure of load balancing across all processes, defined as the maximum number of indices on any process divided by the average number of indices per process. This function calculates the imbalance separately for owned indices and ghost indices and returns them as a std::array<double, 2>. If the total number of owned or ghost indices is zero, the respective entry in the array is set to -1.

Note
This is a collective operation and must be called by all processes in the communicator associated with the IndexMap.
Returns
An array containing the imbalance in owned indices (first element) and the imbalance in ghost indices (second element).

◆ index_to_dest_ranks()

graph::AdjacencyList< int > index_to_dest_ranks ( ) const

Compute map from each local (owned) index to the set of ranks that have the index as a ghost.

Todo
Aim to remove this function?
Returns
shared indices

◆ local_to_global()

void local_to_global ( std::span< const std::int32_t > local,
std::span< std::int64_t > global ) const

Compute global indices for array of local indices.

Parameters
[in]localLocal indices
[out]globalThe global indices

◆ owners()

std::span< const int > owners ( ) const
inline

The ranks that own each ghost index.

Returns
List of ghost owners. The owning rank of the ith ghost index is owners()[i].

◆ shared_indices()

std::vector< std::int32_t > shared_indices ( ) const

Build a list of owned indices that are ghosted by another rank.

Returns
The local index of owned indices that are ghosts on other rank(s). The indices are unique and sorted.

◆ src()

std::span< const int > src ( ) const
noexcept

Ordered set of MPI ranks that own caller's ghost indices.

Typically used when creating neighbourhood communicators.

Returns
MPI ranks than own ghost indices. The ranks are unique and sorted.

The documentation for this class was generated from the following files: